The enzymes from cyanobacteria that belong to the Nostocales order participate in the biosynthesis of hapalindole-type alkaloids. According to the proposed mechanism, the enzyme forms an imine intermediate composed of linked L-tryptophan and D-ribulose 5-phosphate, followed by loss of the phosphate group and formation of a beta-keto imine and keto-enol tautomerization. This is followed by a C-C bond cleavage, the release of hydroxyacetone, and a retro aldol type reaction that releases formaldehyde and forms the final product [3]. cf. EC 4.1.99.24, L-tyrosine isonitrile synthase.